1. Field of the Invention
The present invention relates to a disk drive device that rotationally drives a disk.
2. Description of the Related Art
There are known hard disk drives (HDDs) as media used in storage devices of computers, etc. Such devices for driving recording disks are collectively referred to as disk drive devices. In a disk drive device, a recording disk on which recording tracks for recording magnetic data are formed is rotated at high speed by a brushless motor (hereinafter, simply referred to as a “motor”). A magnetic head for performing read/write of magnetic data stored on the recording disk is arranged above the recording surface of the recording disk so as to create a slight space between the two, and is configured to trace the recording tracks.
A motor of which the disk drive device is composed is generally structured to include: a stator in which an armature coil is provided, a rotor in which a magnet to be arranged so as to face the stator is provided, and a bearing unit configured to rotatably support the rotor relative to the stator. As such motors, there are two types of motors, in one of which the rotor composed of a shaft to be the center of the rotation is rotated while being supported by a sleeve fixed to the stator, and in the other of which the rotor composed of a sleeve is, in contrast, rotated while being supported by a shaft fixed to the stator. The recording disk is fixed to a hub member fixed to the shaft or the sleeve, either of which the rotor is composed of, and is rotated with the hub member at high speed by the drive of the motor. In order to realize high performance of the motor, there are many cases where fluid dynamic bearings are used in the bearing units (see, for example, Japanese Patent Application Publication No. H1-210615).
This fluid dynamic bearing is configured between the aforementioned shaft and sleeve. The shaft has a flange portion at its one end. The sleeve, having a bottomed cylindrical shape, faces in the radial direction the outer circumferential surface of the shaft through a minor space, and also faces in the axial direction the upper surface and the lower surface of the flange portion through a minor space. Oil is injected into each minor space as a lubricant fluid. A pair of radial dynamic pressure corresponding portions, which are spaced apart from each other in the axial direction, are provided on the inner circumferential surface of the sleeve. A radial dynamic pressure groove for generating proper radial dynamic pressure is formed between each radial dynamic pressure corresponding portion and the shaft. On the other hand, thrust dynamic pressure corresponding portions are provided on the upper surface and the lower surface of the flange portion of the shaft. A thrust dynamic pressure groove is formed between each thrust dynamic pressure corresponding portion and the sleeve. When either the shaft or the sleeve starts rotating relative to the other, dynamic pressure is generated in each bearing unit, thereby allowing for the rotor to be rotatably supported in a non-contact state relative to the stator. That is, the rotor is floated by making the pressure in the bearing unit higher than or equal to atmospheric pressure. In recent years, the rotational accuracy of disk drive devices has been drastically improved by comprising these fluid dynamic bearings, thereby allowing for the high density and large capacity of the magnetic data, which can be stored, to be realized. As a result, the disk drive devices have been mounted in various apparatuses, thereby making use environments for the disk drive devices extensive.
Such disk drive devices are demanded to have high reliability regardless of their installation directions, due to the arrangement requirements in accordance with the installation aspects of computers in which the disk drive devices are to be mounted. That is, in the disk drive device provided with such a fluid dynamic bearing, a hub member is generally connected with one end of the shaft or the sleeve, either of which the rotor is composed of. Accordingly, when the shaft is used, in particular, in a horizontal state, the gravity of the hub member is biased to the one end of the shaft, making a so-called cantilever state. Therefore, in particular, when the rotation is stopped in which dynamic pressure does not act, the shaft becomes tilted, causing the tilts of the axes of the shaft and the sleeve to deviate from each other.
The sleeve generally has a slightly tilted structure in which the gap between the radial dynamic pressure corresponding portion and the shaft becomes smaller going from the axial center portion toward the outside of the sleeve, in order to effectively generate dynamic pressure by the shape of the radial dynamic pressure corresponding portion itself and in order not to let out the lubricant. Because the sleeve has such a shape, if the axes of the shaft and the sleeve deviate from each other as stated above, the radial dynamic pressure corresponding portion and the shaft are locally in contact with each other when the rotation is stopped, thereby increasing the surface pressure in the contact portion. That is, in particular, when a disk drive device is installed in a state where the shaft thereof is maintained horizontally, the shaft will be locally in contact with the radial dynamic pressure corresponding portion even if the rotation of the rotor is stopped at any timing, and hence the pressure at the contact is increased. In addition, even if the shaft is not maintained horizontally, local contact pressure, more or less, can be generated when the rotation of the rotor is stopped. Therefore, there has been the problem that, when start/stop of the rotation of the rotor have been repeated in a disk drive device, the radial dynamic pressure corresponding portion is abraded, and accordingly the rotational stability may be impaired and the lifetime of the disk drive device until read/write of data is not performed normally, is shortened.